This invention relates to novel compounds which are effective to improve the heat stability of olefin polymers. It relates more particularly to olefin polymer compositions which contain such novel compounds.
Generally, polymer compositions are vulnerable to deterioration of physical and chemical properties during manufacture, storage, processing and use. To overcome such deterioration, or at least to inhibit it, there have been developed additive systems for the purpose of stabilizing polymeric materials with respect to physical and chemical degradation caused by exposure to environmental conditions. All of these additive systems, however, while effective for their intended purpose, are characterized by one or more shortcomings.
Olefin polymer compositions are especially vulnerable to oxidative degradation. The relatively high temperatures required for their customary processing procedures, such as roll milling, injection molding, extrusion and the like, invariably promote oxidation because these processes are carried out under ordinary atmospheric conditions, i.e., they are exposed to the oxygen of the atmosphere.
The significance of polymer oxidation lies in the adverse effect it has on polymer rheology, morphology, color, clarity, glass and other physical properties. Impact strength may be lost; the surface may become crazed or cracked. Even a darkening of the color may provide a sufficient aesthetic disadvantage as to render the polymer material unsuitable for its intended use.